The aim of this experiment is to determine what affects the rate at which a reaction occurs between sodium thiosulphate and hydrochloric acid.

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Introduction

Chemistry Coursework - Sodium Thiosulphate + Hydrochloric Acid Aim The aim of this experiment is to determine what affects the rate at which a reaction occurs between sodium thiosulphate and hydrochloric acid. I intend to find out whether (and to what degree) varying the concentration of sodium thiosulphate has any effect on the rate of reaction between these chemicals. I believe that these variables are linked, and that the concentration of sodium thiosulphate has a direct effect on the rate at which the reaction occurs. Hypothesis This is the chemical equation for the reaction: Na2 S2 O3 (aq) + 2NaCl (aq) + H20 (l) + SO2 (aq) +S (s) Concentration of a solution refers to the amount of reactant particles that have been dissolved in one unit of that solution. Therefore, the more reactant particles in a solution, the higher the concentration. As you increase the concentration of a solution, there are more reactant particles present in the unit of solution, which is always kept at the same volume. So if there are more reactant particles to the same volume of solution, then the rate of reaction will increase. The rate of reaction increases because if more reactant particles are in a given volume, then there is a greater potential for reactant particles to collide with other reactant particles. The more collisions in a reaction, then the more collisions will be successful, and perform the reaction. A successful collision is determined by whether or not a collision occurs with enough energy to pass through the activation energy barrier. By increasing the reactant particles in a given volume, we are increasing the rate of reaction. ...read more.

Middle

I will keep this constant by using the same black pen to draw the cross each time. Volume Of Sodium Thiosulphate And Hydrochloric Acid - The larger the volume of sodium thiosulphate and/or hydrochloric acid, the greater total number of particles in the solution. This means that to completely react, and go cloudy, it will take longer. I will keep this variable constant by using 50cm� of sodium thiosulphate solution with 5cm� of hydrochloric acid each time. Movement Of Reacting Mixture - If I shake the conical flask while it is reacting, then the reaction may speed up and therefore the rate of reaction would be quicker. Likewise, if I stir it then it will increase the rate of reaction, because there will be a greater chance of the particles colliding with other particles which they can react with because the two types of particles will be more mixed together. Fair Test In order to achieve a fair test, a number of measures must be taken to ensure it. * All measurements must be kept constant and accurate as possible, using correct measuring equipment. * The timing of the reaction will have to be kept as accurate as possible, making sure a stopwatch is used, and start and stop times are as accurate as possible. * The experiment should be performed over the time period of the one day. The changes in atmospheric pressure could result in differing concentrations and anomalous results. There is no way to make this experiment 100% fair, as human judgment is inaccurate, and some slightly anomalous results may occur due to judging whether the water is cloudy yet. ...read more.

Conclusion

Evaluation The results of this experiment appear to be quite accurate and so I can make a definite conclusion. From this, I can speculate that the experiment was conducted well, and that the results have only been affected by other variables by little or no amount. However, looking at the graph, I can see that there are some results, two specifically, that do not follow the general trend, and show a higher or lower rate of reaction than would be expected at that point. I believe that perhaps this was caused by a change in another variable, or an inaccuracy in the measuring of the input variable. Either the reacting mixture was shaken accidentally, moving the molecules around more, increasing their chances of reacting, or more likely, the concentrations of sodium thiosulphate were incorrectly measured, and too much sodium thiosulphate was used. This would reduce the distances between the molecules, and increase the rate of reaction. I think that the only flaws in the experiment were in the measuring of the concentrations, and in the judging of when the reaction had completed. It was very hard to get an exact volume of water/sodium thiosulphate to get the right concentration, and so this may have thrown those three results off the trend. Also, there was not really any sure way of knowing when the reaction had finished. Also, it is quite possible that human judgment might waver slightly when deciding if the reaction has completed yet. If I was to repeat the experiment, I would use a much more accurate way of measuring the volumes of the reactants, and I would find a completely different way of measuring when the reaction has completed. ...read more.

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In this preliminary test I did not stir the solution and this is one thing I do actually intend to change. This is because the rate of reaction occurs faster due to more successful collision rates and therefore a faster rate of reaction.

One of these parts is the measurement of the hydrochloric acid, sodium thiosulphate and the water in the measuring cylinders. I could have used a more accurate measuring cylinder with smaller and more precise measurements so that I could make even more sure that they were the correct measurements and

When the concentration of a solution is high, there is greater amount of particles in it, compared to the amount of particles in a lower concentrated solution. Therefore if we increase the concentration, we increase the number of particles in the solution.

* Start the stopwatch and time the reaction. * Record the time it took to make the cross disappear. * Make sure you wear goggles, as this is a safety issue. The Things That Must Be Kept Constant * The temperature of the thiosulfate solution because the more molecules there

I can prove this by looking at two examples from the graph and comparing them. When the concentration of Na2S203 is 0.05 mol dm-3 the rate of reaction is 0.0115. When the concentration of Na2S203 is 0.10 mol dm-3 the rate of reaction is 0.0228.